Editor’s Note: Today’s caption is the answer to Earth Observatory’s February Puzzler.

The Danube River is the largest in the European Union, its watershed draining 801,463 square kilometers (309,447 square miles) of land across 19 countries. Where that great river reaches the Black Sea, a remarkable delta has formed—the “Everglades” of Europe. The Danube Delta is home to more than 300 species of bird and 45 species of freshwater fish.

The Danube Delta has been home to human settlements since the end of the Stone Age (the Neolithic Period), and the ancient Greeks, Romans, and Byzantines all built trading ports and military outposts along this coast. Today, the border between Romania and Ukraine cuts through the northern part of the delta. The area is a United Nations World Heritage Site, both for its natural and human history, and for the traditional maritime culture that persists in its marshes. All the while, the landscape has been shaped and re-shaped by nature and man.

The image above was acquired on February 5, 2013, by the Advanced Land Imager (ALI) on NASA’s Earth Observing-1 (EO-1) satellite. The Danube Delta has a number of lobes formed over the past several thousand years, and this image is focused largely on the northernmost Chilia (or Kilia) lobe. It is the youngest section of the delta—somewhere between 300 to 400 years old—and lies mostly within Ukraine. Much of the land in the image above is officially considered part of the Danube Biosphere Reserve. (To see more about how the delta formed, click here.)

Near the center of the image, the small city of Vylkove is known as the “Ukranian Venice,” due to its canals. To the lower left, the older Sulina lobe of the delta stretches to the south and further inland into Romania. White and brown curved lines reveal beach ridges and former shorelines, with the whiter ridges composed almost entirely of pure quartz sand in high dunes. To the east of the ridges, most of the landscape is flat marshland that is mostly brown in the barren days of winter.

The Bystroye Canal through the center of the Chilia lobe has been the subject of heated debate over the past two decades. Over the centuries, damming and channeling of the Danube throughout Europe has reduced its water flow and sediment load to roughly 30 percent of what it once was, according to coastal geologist Liviu Giosan of the Woods Hole Oceanographic Institution. In recent years, the Ukrainian government has dredged some delta channels (including Bystroye) and proposed extensive dredging of others in order to provide navigational channels for large ships. Proponents argue for the economic needs of water transportation routes. Opponents note that deeper, faster channels mean less mud and sand is deposited in the delta; in some places, more is carried away by swifter currents. Both affect the sensitive ecosystems and the ability of the delta to restore itself and grow.

In a 2012 report led by Giosan, scientists noted that the shape, water chemistry, and biology of Danube Delta was being altered long before the modern Industrial Era. Land use practices—particularly farming and forest clearing—added significant amounts of nutrients into the water and reduced salinity in the Black Sea, changing the dominant species of phytoplankton and sending a ripple of effects through the entire food web.

NASA Earth Observatory image by Jesse Allen and Robert Simmon, using EO-1 ALI data provided courtesy of the NASA EO-1 team and the U.S. Geological Survey. Caption by Mike Carlowicz. Congratulations to Kevin Martin, CEO/senior meteorologist for TheWeatherSpace.com, for being the first person to solve the puzzler.